The scapula, commonly known as the “shoulder blade”, is a flat, triangular bone that lies over the back of the upper ribs. A left scapula 100 is depicted in anterior, posterior, and left side views in FIGS. 1A, 1B, and 1C, respectively. The posterior surface of the scapula 100 can be readily felt through a patient's skin. The scapula 100 serves as an attachment point for some of the muscles and tendons of the arm, neck, chest, and back, and aids in the movements of the arm and shoulder. The scapula 100 is also well padded with muscle, so that great force is required to fracture it. The rear surface of each scapula 100 is divided into unequal portions by a spine 102. This spine 102 leads to a head 104, which bears two processes—the acromion process 106 that forms the tip of the shoulder and a coracoid process 108 that curves forward and down below the clavicle (collarbone, not shown). The acromion process 106 joins the clavicle and provides attachments for muscles of the arm and chest muscles. The acromion process 106 is a bony prominence at the top of the scapula 100. On the head 104 of the scapula 100, between the acromion and coracoid processes 106 and 108, is a depression or cavity called the glenoid vault 110, shown partially in dashed line in the Figures. The glenoid vault 110 joins with the head of the upper arm bone (humerus, not shown) in a ball-and-socket manner to enable articulation of the shoulder joint thereby formed.
For treatment of various problems with the shoulder, hip, or other body joint or bone (such as degenerative arthritis and/or traumatic injury), one method of providing relief to a patient is to replace the articulating surfaces with an artificial or prosthetic joint. In the case of a shoulder, the humerus and glenoid vault 110 articulating surfaces are replaced. In the case of a hip, the femur and acetabulum articulating surfaces can be replaced. Both of these examples are of ball-and-socket type joints. Hinge-type joints, such as the knee or elbow, and static/fixed skeletal components, such as the long bones of the arm or leg, could also be subject to replacement and/or repair by the implantation of artificial or prosthetic components, as could interfaces such as those between spinal vertebrae and intervertebral discs. For clarity of description, the subject application will be hereafter described as the rehabilitation and/or replacement of a patient's shoulder joint.
In such surgical procedures, pain relief, increased motion, and anatomic reconstruction of the joint are goals of the orthopedic surgeon. With multiple variations in human anatomy, prosthetic systems must be carefully designed and chosen to both accurately replicate the joints that they replace and maintain the natural symmetry of the joints on the left and right sides of the patient's body.
A shoulder replacement procedure may involve a partial shoulder replacement (not shown) or the total shoulder replacement shown in FIG. 2. In a total shoulder replacement procedure, a humeral component 212 having a head portion is utilized to replace the natural head portion of the upper arm bone, or humerus 214. The humeral component 212 typically has an elongated stem which is utilized to secure the humeral component to the patient's humerus 214, as depicted. In such a total shoulder replacement procedure, the natural bearing surface of the glenoid vault 110 is resurfaced, lined, or otherwise supplemented with a cup-shaped glenoid component 216 that provides a bearing surface for the head portion of the humeral component 212.
Standard prosthetic glenoid components 216 are available in a number of different sizes and configurations. However, most are designed for use in an anatomically normal scapula. When the scapula has abnormal pathology due to disease or trauma, the standard glenoid component 216 may be difficult to implant and/or may not enable desired shoulder function, once implanted. The surgeon may thus need to substantially modify the patient's glenoid vault 110 during surgery in an attempt to make the standard glenoid component 216 fit into the glenoid vault. Presurgery planning tools are available to help the surgeon anticipate the changes which will be needed to reform the patient's pathological anatomy. However, the surgeon cannot always readily determine whether even a remodeled glenoid vault 110 will fit as desired with a standard prosthesis because the surgeon does not know how a “normal” glenoid vault 110 (for which the standard prosthesis is designed) should be shaped for that patient.
It is known to use computer aided design (“CAD”) software to design custom prostheses based upon imported data obtained from a computerized tomography (“CT”) scan of a patient's body. For example, mirror-imaged CT data of a patient's contralateral “normal” joint could be used, if the contralateral joint does not also display a pathological anatomy. However, using a unique prosthesis design for each patient can result in future biomechanical problems and takes away the familiarity that the surgeon will likely have with standardized prosthesis designs. Thus, prosthesis designs that are entirely customized are considered sub-optimal solutions.
An example of a customized prosthesis and method of designing and making such using CT data is disclosed in U.S. Pat. No. 6,944,518 (hereafter referenced as “the '518 patent”). The '518 patent discloses a method of making a prosthesis for a joint socket in which CT data from a patient's joint is used to design the prosthesis. The CT data is downloaded into CAD software in order to design at least an attachment part, and possibly a functional part, of the prosthesis. The attachment part can be used to attach or otherwise associate the functional part to the patient's bone. The functional part can have standardized dimensions.
The attachment part of the '518 patent must be custom-made, which adds time and expense to the surgical preparation process. Moreover, biomechanical interaction between the functional prosthesis and the patient's joint will be altered in possibly unpredictable ways by the interposed attachment part. Finally, use of the attachment part prevents the patient's pathological anatomy from being corrected, and may even result in deterioration of the patient's native bone, which could cause further problems with the prosthetic joint and/or could complicate revision surgery.